Organic thin-film solar cells are a well-known type of solar cell and are made using an organic semiconductor.
Organic thin-film solar cells are thinner, lighter, and more flexible than conventional solar cells. Furthermore, organic thin-film solar cells are easier and cheaper to manufacture than inorganic solar cells made from monocrystalline materials or thin-films of silicon or compounds such as GaAs, CIS, or CIGS.
Moreover, manufacturing methods for organic thin-film solar cells are simple because no electrolyte solutions are used during manufacture and the structure of the cells is simpler than in dye-sensitized solar cells (another type of organic solar cell). Organic thin-film solar cells also exhibit advantages in terms of flexibility and lifespan.
In addition, when manufactured using the roll-to-roll method with a high speed rotary printing press, organic thin-film solar cells can be produced at roughly 1/10 the cost of conventional vacuum deposition methods and are believed to be the lowest-cost solar cells that can generate power.
However, in comparison with silicon-type or compound-type inorganic solar cells, organic thin-film solar cells tend to exhibit a lower photovoltaic energy conversion efficiency per unit area because the organic semiconductor materials used therein tend to have a low photovoltaic energy conversion efficiency.
More specifically, in a conventional organic thin-film solar cell, when the cell is irradiated with sunlight, that light first has to pass through components such as the anode (which is a transparent electrode) before reaching an organic semiconductor layer. The light that passes through the organic semiconductor layer reaches a cathode which is made from a metal, reflects off of the metal cathode, and passes through the organic semiconductor layer again before escaping out of the cell.
This light that passes through the organic semiconductor layer is converted to photovoltaic energy. However, the photovoltaic energy conversion efficiency of organic semiconductor materials is less than that of inorganic semiconductor materials such as silicon that are already used widely, and as a result, the photovoltaic energy conversion efficiency of the overall organic thin-film solar cell is less than that of an inorganic solar cell.
Despite having many advantages as described above, organic thin-film solar cells tend to exhibit a low photovoltaic energy conversion efficiency. Therefore, there is high demand for development of organic thin-film solar cells that have a higher photovoltaic energy conversion efficiency and still allow all of the abovementioned advantages to be utilized.
It should also be noted that as of the time of this filing, the only prior art known to the present applicant are those technologies described above. Technologies analogous to the present invention have not previously been disclosed, and therefore there are no prior art documents that should be cited here.